The rotating field of an electrical machine is normally produced by a rotor which has slots in which electrical conductors are located. The rotor core is normally in this case manufactured from steel, while the turns are produced from copper or from some other electrically conductive material. The inducing field is produced by passing direct current through these turns which direct current is either produced separately and is supplied to the conductors via brushes on the rotor shaft, or is produced directly on the shaft for so-called brushless excitation.
Owing to the high centrifugal forces which occur during operation of a rotor such as this, it is important for the conductors to be firmly wedged to the rotor core. On the other hand, it is important to efficiently dissipate the heat which is produced during operation, that is to say to ensure good cooling for the conductors.
This is normally achieved by providing slots in the rotor core, by then inserting two or more conductors one above the other and possibly also alongside one another into these slots, and by then using wedges to close the peripheral face of the slots and to secure the conductors by means of the wedges in the slots. In this case, the conductors are surrounded by an insulation layer. Alternatively, it is possible not to provide any wedges but in fact to provide rings which surround the rotor circumferentially and hold the conductors in the slots. In other words, the conductors are pressed radially towards them by the wedges or the rings, thus absorbing the centrifugal forces.
The cooling of arrangements such as these is normally made possible by providing cooling channels either in the conductors or between the conductors, and by circulating cooling gas or some other cooling medium through these cavities during operation.
Rotor geometries such as these are described, for example, in CH 638349 or CH 649422.
Arrangements such as these are subject to the problem that turns shorts occur frequently, caused by the insulation which is provided between the conductors being rubbed off and them then being mechanically so severely loaded by the powerful centrifugal forces during operation that the insulation effect is no longer ensured.